PURPOSE: To purify waste water by dividing a water tank in four sections, the first section having a partition provided in the center and the other three sections containing a cartridge filled with active carbon and floatstones arranged alternately over the other.

CONSTITUTION: A water tank A is divided in four sections, the first section having a partition B provided in the center for receiving waste water. In addition, a hole is bored above the partition B to allow the waste water to run into two sections. A cartridge C filled with active carbon and floatstones arranged alternately over the other is placed in the second to the fourth section. The arrangement of active carbon and floatstones in each cartridge varies slightly according to the section. Further, water flows from top to bottom in the second section, from bottom to top in the third section and from top to bottom in the fourth section. Under the above-mentioned structural design, the waste water is purified and then is discharged into a drain pipe. The cartridge is replaced twice a year and the recovered active carbon and floatstones can be purified for recycled use several times.